A callback for ActiveRecord database connections?

Question

Is there any way to hook into ActiveRecord connection creation? I want to run some code whenever a connection has just been created.

I feel like it might be a way to set a MySQL variable on the connection, since "variables" in database.yml doesn't seem to work for me. (How to turn off MySQL strict mode in Rails)

Answer 1

The ConnectionAdapter defines two callbacks :checkout (connect) and :checkin (disconnect). You can use it for specific adapter as

ActiveRecord::ConnectionAdapters::MysqlAdapter.set_callback :checkout, :after do
  raw_connection.set_your_variables ...
end

Or you can use ActiveRecord::Base.connection.class for whatever adapter is currently declared in database.yml

Answer 2

Also, if you need to configure your model after connection has been made and column information was retrieved, you can redefine load_schema! class method in model.

See: https://github.com/rails/rails/pull/31681#issuecomment-357113030